n = int(input())
c = list(input())

r = 0
temp = 0

for i in c:
    if i == 'R':
        r += 1
    
w = n - r

for i in range(r):
    if c[i] == 'R':
        temp += 1

print(r - temp) n = int(input()) n int(input()) int input() input c = list(input()) c list(input()) list input() input r = 0 r 0 temp = 0 temp 0 for i in c:
    if i == 'R':
        r += 1
     i c if i == 'R':
        r += 1
     i == 'R' i 'R' r += 1 r 1 w = n - r w n - r n r for i in range(r):
    if c[i] == 'R':
        temp += 1 i range(r) range r if c[i] == 'R':
        temp += 1 c[i] == 'R' c[i] c i 'R' temp += 1 temp 1 print(r - temp) print r - temp r temp n = int(input()) int(input()) n temp = 0 0 temp c = list(input()) list(input()) c r += 1 1 r w = n - r n - r w r = 0 0 r temp += 1 1 temp
n = int(input())
c = list(input())

r = 0
temp = 0

for i in c:
    if i == 'R':
        r += 1
    
w = n - r

for i in range(r):
    if c[i] == 'R':
        temp += 1

print(r - temp)